As the density of semiconductor devices increases and the size of circuit elements becomes smaller, the resistance capacitance (RC) delay time increasingly dominates the circuit performance. To reduce the RC delay, there is a desire to switch from conventional dielectrics to low-k dielectrics. These materials are particularly useful as intermetal dielectrics, IMDs, and as interlayer dielectrics, ILDs. However, low-k materials present problems during processing, especially during the processing of the conductive material used to make interconnects.
The conductive material is typically patterned and etched using high-energy plasma etch processes. In other process schemes, the low-k material is patterned through the application and patterning of photoresist. The low-k material is etched through the photoresist mask, and then the photoresist is removed with a high energy plasma etch process. The low-k materials are susceptible to damage from a plasma etch because they are softer, less chemically stable, or any combination of these factors. The plasma damage can manifest itself in higher leakage currents, lower breakdown voltages, and changes in the dielectric constant associated with the low-k dielectric material.
One example of low-k dielectrics are porous dielectric materials. The porous low-k dielectric is typically formed from a low-k precursor material comprised of a thermally cured matrix material and a thermally degradable porogen material. Typically, a spin-on process applies a solution of the uncured, low-k, precursor material, and then a thermal process cures the low-k precursor material to form the low-k dielectric material. The curing process, which may include one or more processing steps, typically cross links the matrix and forms pores by thermally degrading the porogen. During curing, the porogen forms volatile by-products that diffuse out of the low-k dielectric material leaving nanopores in their place.
Waldfried et al. in U.S. Pat. No. 6,756,085 disclose that ultraviolet (UV) curing decreases the curing time, increases the elastic modulus, and increases hardness of dielectric materials. Waldfried et al., in U.S. Patent Application Publication No. 2004/0058090, disclose that the benefits of UV curing extend to porous dielectric materials.
Despite recent advances, however, integration of porous dielectrics into conventional device fabrication schemes has created new problems. The open and interconnected porosity of the dielectrics allow reactive gases and chemicals to easily penetrate into the porous structure and damage the bulk material. Particularly degrading processes are photoresist removal and metal deposition. Moreover, the introduction of nanopores often deteriorates the mechanical properties of the film thereby limiting the yield of chemical mechanical polishing in copper-ELK (extreme low-k dielectric) process integration.
To overcome these and other problems, new and improved manufacturing methods are needed in order to realize the full advantages of porous, low-k dielectrics.